Add WorkingCopy::merge() to support git merge

doc/workingcopy.md

@@ -26,6 +26,24 @@ $wc->checkout('origin/master', 'master');
 
 You can also pass a *Reference* or a *Commit*.
 
+Merge a revision
+----------------
+
+You can merge any revision into the current branch using the *merge* method.
+A second argument can be used to pass extra options to the underlying
+`git merge` command:
+
+```php
+// git merge origin/develop
+$wc->merge('origin/develop');
+
+// git merge --no-ff origin/develop
+$wc->merge('origin/develop', ['--no-ff']);
+```
+
+You can also pass a *Reference* or a *Commit*. A `RuntimeException` is thrown
+if the merge fails (for instance because of a conflict).
+
 Staged modifications
 --------------------
 

src/Gitonomy/Git/WorkingCopy.php

@@ -101,6 +101,29 @@ public function checkout($revision, ?string $branch = null): static
         return $this;
     }
 
+    /**
+     * Merges a revision into the current branch.
+     *
+     * @param Commit|Reference|string $revision
+     * @param string[]                $args     extra arguments for the merge command (e.g. ``['--no-ff']``)
+     */
+    public function merge($revision, array $args = []): static
+    {
+        if ($revision instanceof Commit) {
+            $args[] = $revision->getHash();
+        } elseif ($revision instanceof Reference) {
+            $args[] = $revision->getFullname();
+        } elseif (\is_string($revision)) {
+            $args[] = $revision;
+        } else {
+            throw new InvalidArgumentException(\sprintf('Unknown type "%s"', \gettype($revision)));
+        }
+
+        $this->run('merge', $args);
+
+        return $this;
+    }
+
     private function run(string $command, array $args = []): ?string
     {
         return $this->repository->run($command, $args);

tests/Gitonomy/Git/Tests/WorkingCopyTest.php

@@ -110,4 +110,30 @@ public function testGetUntracked(): void
 
         $this->assertContains('untracked.txt', $wc->getUntrackedFiles());
     }
+
+    public function testMerge(): void
+    {
+        $repository = self::createFoobarRepository(false);
+        $repository->run('config', ['--local', 'user.name', '"Unit Test"']);
+        $repository->run('config', ['--local', 'user.email', '"unit_test@unit-test.com"']);
+        $wc = $repository->getWorkingCopy();
+        $wc->checkout('master');
+
+        $wc->merge('origin/diff-features');
+
+        $head = $repository->getHeadCommit();
+        $this->assertCount(2, $head->getParents(), 'Merge produced a merge commit');
+        $this->assertFileExists($repository->getWorkingDir().'/script_A.php');
+    }
+
+    public function testMergeConflict(): void
+    {
+        $this->expectException(RuntimeException::class);
+
+        $repository = self::createFoobarRepository(false);
+        $wc = $repository->getWorkingCopy();
+        $wc->checkout('master');
+
+        $wc->merge('origin/new-feature');
+    }
 }